The present invention relates to magnetic heads for data storage, and more particularly, this invention relates to adhesives having electrostatic discharge (ESD) dissipating properties for use with magnetic heads.
In magnetic storage systems, data is commonly read from and written onto magnetic recording media utilizing magnetic transducers. Data is written on the magnetic recording media by moving a magnetic recording transducer to a position over the media where the data is to be stored. The magnetic recording transducer then generates a magnetic field, which encodes the data into the magnetic media. Data is read from the media by similarly positioning the magnetic read transducer and then sensing the magnetic field of the magnetic media. Read and write operations may be independently synchronized with the movement of the media to ensure that the data can be read from and written to the desired location on the media.
Magnetoresistive (MR) sensors, such as giant magnetoresistive (GMR), anisotropic magnetoresistive (AMR) and tunnel valve magnetoresistive (TMR) sensors, are used to read data written on magnetic media. MR sensors are used extensively in the hard disk drive (HDD) and tape drive industries. MR sensors are highly sensitive to damage by ESD events. This is a major problem that is encountered during manufacturing, due to handling and use of MR sheet resistors with the build-up of electrostatic charges on the various components of a head or other objects which come into contact with the MR sensors and spontaneously discharge through the MR sensor leading to damage. Static charges may be externally produced and accumulate on instruments used by persons performing head manufacturing or testing function. These static charges may also discharge through the head, causing physical and/or magnetic damage to the sensors.
One method to prevent or minimize ESD damage to MR sensors is via diode protection. Generally, the best location to attach the diodes for maximum protection is as close to the sensors as possible. In tape and HDDs, typically a flexible cable is attached to the MR sensors to allow a connection to external electrical devices. The cabled sensor modules (CMODs) are then assembled into a magnetic head which includes an actuator to move the sensor over the particular data track to be read. The actuation is high frequency, and the response of the actuation is slowed down by extra mass and cable rigidity, urging the use of smaller and smaller cables. In attaching the cables, the spacing between the cable leads can vary along the length of the cable. Furthermore, the spacing of the leads on the cable may change from one product to another. In addition, there are several manufacturing steps required to attach the diode(s) to the MR sensor, thus the possibility still exists for ESD damage to the MR sensor during any of these steps prior to the diode being attached.
Another method to prevent or minimize ESD damage to MR sensors is via conductive coatings. In prior art attempts, these coatings have been applied through screen-printing, rotogravure, and syringe dispensing. They have typically provided good adhesion, but are highly viscous (greater than about 20,000 CP) and therefore are inherently difficult to apply and place with any level of accuracy.
In any of the methods used in preventing or minimizing ESD damage to MR sensors using a conductive coating suffer from frequent agglomerates of conductive particles compromising the coating. In particular, these agglomerates form conductive bridges whenever the agglomerate spans the lead-to-lead spacing of the cable, negating the protective advantages conferred by the coating. Furthermore, as feature size, including lead-to-lead spacing, continues decreasing with advancing component technology, the likelihood of such agglomerates conferring inadequate protection or producing catastrophic failure increases, ultimately making the conventional conductive coating an inadequate solution.